Polysiloxane-diamine modified gel as precursor to crystalline/amorphous Si3N4

New hybrid organic-inorganic materials are prepared by reaction of polymethylhydrosiloxane (PMHS) with aniline (An) or 4,4′-diamino,diphenyl methane (APM) through a condensation between NH2-terminated amines and Si—H groups. The obtained modified-polysiloxane is a liquid polymer (PS-An) in the first case and a cross-linked gel (PS-APM) in the second one. The chemical structures of PS-An and PS-APM were investigated by 29Si nuclear magnetic resonance and were proved to be formed of created (≡Si—O)2(Me)Si—N(H)— and unreacted (≡Si—O)2(Me)Si—H sites. The pyrolysis of the diamine-based gel has been carried out in N2 atmosphere up to 1450°C. FTIR, 29Si MAS NMR and X-ray diffraction have shown that Si—O and Si—C bonds are totally broken during pyrolysis and that the final product is formed of crystalline and amorphous silicon nitride in the presence of a free carbon phase.